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The effects of winter stress on Sphagnum specieswith contrasting macro- and microdistributions
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution. (Rydin)ORCID iD: 0000-0002-4642-4066
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.ORCID iD: 0000-0002-7582-3998
2019 (English)In: Journal of Bryology, ISSN 0373-6687, E-ISSN 1743-2820, Vol. 41, no 3, p. 205-217Article in journal (Refereed) Published
Abstract [en]

Introduction: Sphagnum L. forms much of the ground cover in northern peatlands. Different species show affinities for bioclimatic regions in Europe (oceanic/continental; northern/southern) and species-specific tolerance of winter conditions can be a factor explaining their distribution.

Methods: We focussed on low temperature in a series of experiments and tested (1) the innate ability of a selection of Sphagnum species to tolerate low temperature in relation to their micro-topographic (wetness) and geographical (climate) distribution; (2) the rate of cold tolerance acquisition; and (3) the ability of species to survive a range of low temperature once cold hardened.

Key results: Our experiments showed that maximal PSII efficiency (Fv/Fm, chlorophyll fluorescence), growth rates and survival were all negatively affected by sub-zero temperatures. Environmental conditions associated with the onset of winter (colder nights and shorter days) triggered the acquisition of cold tolerance in Sphagnum.

Conclusions: The results were not unequivocal, but species associated with colder climates were generally more tolerant of sub-zero conditions. Species associated with the wettest and driest ends of the wetness gradient were more consistent in their responses than those in between, with wetter-dwelling species being less sensitive to sub-zero temperature than species found in drier microhabitats. Overall, our results suggest that adaptation to winter conditions contribute to the current distribution patterns of Sphagnum species.

 

Place, publisher, year, edition, pages
Taylor & Francis, 2019. Vol. 41, no 3, p. 205-217
Keywords [en]
Chlorophyll fluorescence, cold tolerance, species distribution, Sphagnum, winter
National Category
Ecology Evolutionary Biology Botany
Identifiers
URN: urn:nbn:se:uu:diva-387429DOI: 10.1080/03736687.2019.1626167ISI: 000473871600001OAI: oai:DiVA.org:uu-387429DiVA, id: diva2:1328957
Funder
Swedish Research Council, 2015-05174Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-10-30Bibliographically approved
In thesis
1. Sphagnum limits: Physiology, morphology and climate
Open this publication in new window or tab >>Sphagnum limits: Physiology, morphology and climate
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sphagnum is the most important plant genus in terms of terrestrial carbon cycling. It and the habitats it creates store an equivalent of ~68% of the CO2 in the atmosphere. The genus has little dispersal limitation and the mire habitats are functionally similar at global scales. Sphagnum species are limited by water deficit at local and biogeographic scales, but this alone is not sufficient to explain local and global scale species patterns. As Sphagnum shoots are long-lived they may be limited by stochastic periods of cold temperature. Within Europe, species are associated with climate gradients along north-south (cold-warm) and oceanic-continental (wet-dry) clines. Within mires, species are sorted along a moisture (hummock-hollow) gradient.

In this thesis I examined species responses to and recovery from freezing (I). I compared species with different water level niches in traits related to water management of individual shoots and colonies (II). Using distribution modelling of GBIF data, I estimated how different aspects of climate contributed to Sphagnum species distributions in Europe (III). Combining the approaches in papers II and III, I modelled the climatic distributions of the parapatric species S. cuspidatum and S. lindbergii and assessed how traits of water economy varied across the distribution boundary (IV).

Species responses to winter stress were largely allied to both their hydrological niche and geographic range. Generally, hollow species managed better than hummock species, but species from intermediate positions were less consistent in their response. Species associated with boreal regions were generally less affected than those from temperate regions. Hardening against low temperature was triggered by shorter days and cold nights. Cold temperatures during late autumn may be more important for Sphagnum limits than the minimum temperature during winter.

Water-related traits split the species into two groups; hollows species with large capitula and hummock species with small capitula. However, inter- and intra-specific trait variation and trait trends along the hydrological gradient were not necessarily the same at the shoot and canopy scale. Some trait correlations were common to all species. Canopy traits, which were emergent traits of colonies of shoots, had the strongest trait associations with the species position along the hummock-hollow gradient.

At the continental scale the distribution of most Sphagnum species could be successfully modelled by a combination of annual degree days and water balance and the degree of seasonality in these two variables. Individual species distributions were shaped more by the seasonality in degree days than in water balance.

Across the distributional border of S. cuspidatum and S. lindbergii divergence in the measured traits was mostly seen in the capitula indicating that limits to Sphagnum species are strongly linked to the functioning of the capitulum. Capitulum mass of both species was lower in sympatry than in allopatry, even though the measured values were similar. Canopy traits most strongly separated the species though did not change across the species boundaries.

In summary, Sphagnum species in general are limited by the availability of water. Low temperature, particularly during late autumn are probably decisive for the biogeographic limits and for the distribution of species along the hydrological gradient.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 40
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1826
Keywords
Sphagnum, ecology, bryophyte, winter, species distribution models, low temperature, plant structure, water economy
National Category
Ecology Botany
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-387444 (URN)978-91-513-0693-3 (ISBN)
Public defence
2019-09-13, Zootissalen, EBC, Villavägen 9, Uppsala, 10:30 (English)
Opponent
Supervisors
Available from: 2019-08-19 Created: 2019-06-24 Last updated: 2019-09-17

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